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Biomedical subjects

G Majno

Publications and source records attributed to G Majno.

At least 19 recordsLinked to original sources
PubMed1999

Lipid deposition in rat aortas with intraluminal hemispherical plug stenosis. A morphological and biophysical study.

A new method was devised to create a stenosis in the rat abdominal aorta. To restrict blood flow, a hemispherical plug was inserted into the aorta through a renal artery. This type of intrinsic (intraluminal) stenosis minimizes possible intramural effects associated with external compression or ligation which severely deform the arterial wall. In the aorta of hypercholesterolemic rats, lipid deposits were distributed in crescent-shaped patches proximal and distal to the plug, whereas lipid deposition in the opposite aortic wall was inhibited. Based on enlarged physical scale models used to study the flow field, the regions of lipid deposition were found to coincide with regions of low shear stress, stagnation, and recirculation. Shear stress was elevated at the wall opposite the plug. These results show that when confounding mural effects are minimized, lipid deposition is promoted in regions of low shear stress with recirculation and inhibited in regions of elevated shear stress.

Animals↗
PubMed1996

Anti-endothelial cell autoantibodies in BB rats with spontaneous and induced IDDM.

Anti-endothelial cell (anti-EC) antibodies occur in several autoimmune diseases, including human IDDM, but the time course of their development and their importance in disease pathogenesis are unknown. To study such antibodies further, we investigated the BB rat model of autoimmunity. Diabetes-prone (DP) BB rats spontaneously develop autoimmune diabetes, whereas coisogenic diabetes-resistant (DR) BB rats are disease free but can be induced to become diabetic by the depletion of T-cells expressing the RT6 alloantigen. Anti-EC autoantibodies were readily detectable in both untreated DP-BB rats and RT6-depleted DR-BB rats before the onset of diabetes. Their concentration increased with time. The anti-EC antibodies in DP-BB rats were almost exclusively of the IgG2b subclass, whereas those in RT6-depleted DR-BB rats included both the IgG1/2a and the IgG2b subclasses. We also found that intravenous injections of purified immunoglobulins from RT6-depleted DR-BB rats induced abnormal pancreatic vascular leakage in mice. The preabsorption of immunoglobulins against cultured ECs abolished this activity. The pretreatment of mice with silica also abolished the ability of immunoglobulins of RT6-depleted DR-BB rats to induce pancreatic leakage, suggesting that monocytes are involved in the mechanism of anti-EC autoantibody-induced vascular leakage. We conclude that anti-EC autoantibodies are present in rat strains that are genetically predisposed to develop autoimmune diabetes. Their presence early in the disease process and their ability to induce pancreatic vascular leakage suggest that they may participate in diabetes pathogenesis.

Adipose Tissue↗
PubMed1995

Apoptosis, oncosis, and necrosis. An overview of cell death.

The historical development of the cell death concept is reviewed, with special attention to the origin of the terms necrosis, coagulation necrosis, autolysis, physiological cell death, programmed cell death, chromatolysis (the first name of apoptosis in 1914), karyorhexis, karyolysis, and cell suicide, of which there are three forms: by lysosomes, by free radicals, and by a genetic mechanism (apoptosis). Some of the typical features of apoptosis are discussed, such as budding (as opposed to blebbing and zeiosis) and the inflammatory response. For cell death not by apoptosis the most satisfactory term is accidental cell death. Necrosis is commonly used but it is not appropriate, because it does not indicate a form of cell death but refers to changes secondary to cell death by any mechanism, including apoptosis. Abundant data are available on one form of accidental cell death, namely ischemic cell death, which can be considered an entity of its own, caused by failure of the ionic pumps of the plasma membrane. Because ischemic cell death (in known models) is accompanied by swelling, the name oncosis is proposed for this condition. The term oncosis (derived from ónkos, meaning swelling) was proposed in 1910 by von Reckling-hausen precisely to mean cell death with swelling. Oncosis leads to necrosis with karyolysis and stands in contrast to apoptosis, which leads to necrosis with karyorhexis and cell shrinkage.

Animals↗
PubMed1992

Acute endothelial cell contraction in vitro: a comparison with vascular smooth muscle cells and fibroblasts.

The contractile responses of cultured rat and calf endothelial cells (EC), vascular smooth muscle cells (VSMC), and fibroblasts (FB) to vasoactive mediators (thrombin, serotonin, bradykinin, and histamine), forskolin, and cytochalasin B were compared. Cells were grown on a pliable silicone membrane, and contraction was assessed, using time-lapse video microscopy, by recording changes in the wrinkling of the silicone as the cells exerted tension on the surface. We found that all cells contracted in the presence of serum or thrombin and that VSMC and FB also contracted with serotonin stimulation. Bradykinin and histamine were not contractants in this system. Discrepancies between these results and reports of changes in permeability of endothelial layers in vitro and in vivo may be due to (1) the vascular segment from which EC were studied or (2) the possibility that certain mediators may provoke a noncontractile response that results in gap formation. Thus changes in vascular permeability, which occur during inflammation, may have both contractile and noncontractile components. Forskolin, known to indirectly inhibit myosin light-chain kinase activity, and cytochalasin B were potent relaxants, suggesting a similar smooth muscle-like contractile mechanism for all three cell types.

Actin Cytoskeleton↗
PubMed1992

Maude Abbott Lecture--1991. The capillary then and now: an overview of capillary pathology.

The concept of capillary is traced through its historical development, beginning with the pathologic "synanastomoses" between arteries and veins as proposed by the ancient Greeks. Harvey assumed that arteriovenous connections existed but never saw them. Malpighi and van Leeuwenhoek were the first to observe the capillary circulation in vivo. In the 1800s, pathologists contributed two advances: a method for proving that capillaries have a structured wall (von Recklinghausen) and the notion of "capillary leakage" in inflammation (Cohnheim). Then physiologists took over for half a century (Starling, Krogh, Pappenheimer) until electron microscopy created a new viewpoint (Palade). Several topics of capillary pathophysiology are discussed: vascular labeling and the capillary as a privileged vessel; capillary versus venular leakage in inflammation; endothelial tone. The overview concludes with a summary of 15 pathologic events that may occur in capillaries.

Anatomy↗
PubMed1991

Lipid deposition and intimal stress and strain. A study in rats with aortic stenosis.

These experiments were designed to study the topography of lipid deposition in the stenotic aorta of hypercholesterolemic rats, and to correlate it with flow conditions and intimal stresses and strains studied in a scale biophysical model and in a computer model. A 69% +/- 5% stenosis was produced with a U-shaped metal clip. One month to 8 months later, the aorta was studied en face by light microscopy after fixation and lipid staining. The intima in the throat of the stenosis was almost completely free of lipid, whereas symmetric lipid deposits occurred as bands just above and especially just below the stenosis; elsewhere lipid deposits appeared to be random. The flow data obtained from the scale model showed that the intima in the throat of the stenosis was subjected to an increase of as much as 20 times in shear stress, whereas the lipid deposits just above and just below the stenosis were associated with asymmetric flow conditions: the proximal area corresponded to a region of rapidly increasing shear stress, the distal area to a region of low to normal shear stress and separated flow. A finite element computer model based on the aortic deformations indicated that the endothelium at the inlet and outlet of the stenosis is subjected to a symmetric pattern of elevated stresses and strains. These results indicate that 1) the pattern of lipid deposition can not be adequately explained by a hypothesis based solely on flow conditions, and 2) lipid deposits can develop in areas of increased fluid shear stress, decreased fluid shear stress, and increased intimal strains.

Animals↗
PubMed1990

Morphological and physiological characteristics of pancreas-specific venular permeability induced by Monastral blue B.

Leaky blood vessels in the microcirculation can be detected in vivo by injecting an animal with colloidal pigments such as Monastral blue B (MbB) or carbon black. We have previously used the MbB labeling method in the spontaneously diabetic BB/W or rat and detected increased vascular permeability restricted to the venules of the pancreas. We now report the morphological and physiological characteristics of this phenomenon in additional rat strains. Susceptibility to pancreatic labeling with MbB among strains was found to be a highly variable, heritable characteristic, but in no strain did vessels label in any organ other than the pancreas. Pancreatic labeling by MbB was dose dependent, was observed in both inbred and outbred rats, and was not related to major histocompatibility complex haplotype. Enhanced permeability was induced by MbB within minutes of its administration as a result of the formation of gaps between endothelial cells; these gaps then closed within 15 min. Pretreatment with silica or carrageenan, agents known to affect macrophage function, completely blocked pancreatic MbB venular labeling, but the effect was reversible over a period of several days. We hypothesize that presence of MbB in the pancreatic circulation induces organ-specific venular leakage either by a direct effect on pancreatic endothelial cells or via the local release of a mediator.

Animals↗
PubMed1990

Capillary leakage in inflammation. A study by vascular labeling.

The local injection of pure inflammatory mediators induces venular leakage. To test the effect of endogenous mediators from dying tissue on vascular leakage, the authors devised an experimental model simulating an infarct, whereby living vessels would be exposed to fragments of organs undergoing aseptic necrosis. Tissues from donor rats were implanted aseptically in the cremasteric sac. Control rats were implanted with materials deemed to be as close as possible to nonirritating: boiled tissues and spheres of Teflon or glass. At different points the rats were injected intravenously with carbon black and killed an hour later. Whole cremaster mounts showed that vascular labeling was strictly venular up to 8 hours, mixed with capillary labeling between 12 and 24 hours, and mainly or exclusively capillary at 48 hours. Histology showed an acute inflammatory infiltrate in the labeled areas. A similar but weaker labeling pattern accompanied by milder inflammation was seen in controls. These results indicate that the vascular leakage in aseptic inflammation is biphasic, first venular, then capillary; and that the capillary phase is induced by the inflammatory reaction itself, possibly through a form of diffuse angiogenesis.

Animals↗
PubMed1989

Quantitation of oil red O staining of the aorta in hypercholesterolemic rats.

A technique is described which provides morphologic and quantitative data on the amount of oil red O (ORO) staining in thoracic aortas of rats fed a high cholesterol diet. Samples are stained with ORO, the dye is extracted, and the concentration of ORO in the extract is measured colorimetrically. Wistar rats fed ad libitum either standard chow (control group: n = 15) or chow supplemented with 4% cholesterol, 1% cholic acid, and 0.5% thiouracil (CCT group: n = 23) were maintained on these diets for 1, 3, 6, 9, or 12 months. Plasma cholesterol levels averaged overall 87 and 737 mg/dl for the control and CCT groups, respectively. Animals were killed under anesthesia by perfusion fixation with formalin or glutaraldehyde, and samples of thoracic aorta were stained with ORO. After microscopic study en face and measurement of surface area, the ORO was extracted in chloroform-methanol (2:1). Concentrations of ORO (microM) were determined from a standard curve and expressed as microM/mm2 of aorta. Aortas of CCT animals showed progressive diet- and time-dependent increases in the amount of ORO staining compared to controls. We conclude that this method yields reliable quantitative data applicable to studying atherosclerosis in small animals.

Animals↗
PubMed1989

The myofibroblast. Possible derivation from macrophages in xanthogranuloma.

The myofibroblast, a cell with features of both fibroblasts and smooth muscle cells, was described originally in granulation tissue. Since then it has been seen in various neoplastic and nonneoplastic conditions. However, there are still unanswered questions regarding the origin of the myofibroblast. Although the cell's derivation from fibroblasts seems clearly established, it has been proposed that these cells arise from the peritoneal macrophages around free-floating intraperitoneal blood clots in rats. We have studied a case of juvenile xanthogranuloma by light and electron microscopy. The histologic features were typical, although the Touton type of giant cells were uncommon. Electron microscopy showed lipid-containing macrophages; many of these also contained the transversely banded bundles of fibrils characteristic of myofibroblasts. These findings support the macrophage origin of myofibroblasts in humans.

Cell Differentiation↗
PubMed1988

Venular endothelium in vitro: isolation and characterization.

The structural and functional properties of the endothelium vary in relation to anatomic site and position along the vascular tree. Cultures of endothelial cells have been obtained so far from large arteries, large veins and capillaries, but not from venules. We now report techniques for culturing not only rat arterial and venous endothelium, but also a special method for obtaining and culturing venular endothelium. The technique is based on the principle of "vascular labeling," whereby an insoluble pigment can be permanently deposited in the wall of the venules, making them easily visible by light microscopy. The venules of a rat cremaster muscle are labeled with a local injection of histamine followed by Monastral blue B intravenously (i.v.); 24 hours later selected venules are isolated by microdissection and either enzymatically dispersed or placed directly into tissue culture wells. The wells are coated with fibronectin and laminin and supplemented with DMEM, 20% fetal calf serum, and endothelial cell growth factor. Polygonal and spindly endothelial cells begin as clusters, grow in sheets, and sometimes form tubes. The cells stain variably for Factor VIII-related antigen, Ulex Europeus I lectin, and non-muscle specific actin. They synthesize angiotensin-converting enzyme, but do not metabolize acetylated LDL. Ultrastructurally, they display pinocytic vesicles, microtendons, and tight junctions, but not Weibel-Palade bodies. We believe that this method will be important for studying the pathophysiology of venules, which are the preferential target of inflammatory mediators and the typical site of inflammatory cell diapedesis.

Actins↗
PubMed1988

Intimal changes in the aorta of prehypertensive rats.

Intimal changes were quantitated in several rat models of arterial hypertension. One kidney-one clip rats drinking water (1K-1C-water), one-kidney rats treated with deoxycorticosterone acetate and drinking 1% NaCl (1K-DOCA-salt), and two-kidney rats drinking 1% NaCl (2K-salt) were studied after 1 to 8 weeks. The thoracic aorta was examined en face and by electron microscopy. Surprisingly, all 2K-salt, most 1K-DOCA-salt (17 out of 19), and two-thirds of 1K-1C-water rats (12 out of 18) had normal arterial pressure at sacrifice. In these normotensive 2K-salt, 1K-1C-water, and 1K-DOCA-salt animals, intimal mononuclear cells (which emigrated from the blood) increased between three- and ninefold. In these same normotensive 1K-1C-water and 1K-DOCA-salt rats, endothelial cell mitoses increased three- to sixfold with a corresponding increase in endothelial cell numbers. In the latter two groups, there was no evidence of endothelial cell denudation or changes in aortic circumference, and the subendothelial space widened mainly with reticular basement membrane presumably synthesized by the endothelium. In normotensive 1K-DOCA-salt rats, most of the endothelial cells were thick and there were several intercellular gaps. Endothelial proliferation, synthesis of macromolecules, and gap formation, as well as increased mononuclear cell emigration, indicate functional changes in mononuclear cells and in endothelial cells. We suggest that the experimental procedures designed to produce hypertension also generate factor(s) which activates mononuclear cells and/or endothelial cells. This cellular activation leads to intimal changes independent of hypertension.

Animals↗
PubMed1988

Endothelial adaptations in aortic stenosis. Correlation with flow parameters.

A 69 +/- 5% stenosis was produced in the rat aorta, with the purpose of correlating endothelial changes with local flow patterns and with levels of shear stress; the hydrodynamic data were obtained from a scaled-up model of the stenosed aorta. In the throat of the stenosis, where shear stress values were 15-25 times normal, the endothelium was stripped off within 1 hour. It regenerated at half the rate of controls but modulated into a cell type that could withstand the increased shear stress. Adaptations included changes in cell orientation, number, length, width, thickness, stress fibers, and anchoring structures, as well as changes in the length, argyrophilia, and permeability of the junctions. Areas of either elongated or "polygonal" cells consistently developed at the same sites in relation to the stenosis, but the hydrodynamic data showed that they did not always correspond (as had been anticipated) to high and low shear, respectively. It is concluded that endothelial cell shape in the living artery must be determined by some other factor(s) in addition to shear stress.

Actins↗